Vessel for pneumatically mixing powdered or granular material

ABSTRACT

A vessel is used for pneumatically mixing powdered or granular material, containing an elevating tube consisting of two individual tubes beneath which a gas inlet is arranged, the lower individual tube forming an annular channel with the wall of the vessel and, in the event of a given drop in pressure in the elevating tube, the length of this annular channel is adapted to the pressure drop in the elevating tube in such a way that at least substantially the same pressure drop which prevails over the length of the elevating tube, prevails over the length of the annular channel.

[451 Mar. 18, 1975 VESSEL FOR PNEUMATICALLY MIXING POWDERED 0R GRANULAR MATERIAL [75] Inventor: Arnon Wolilfarth,Nachlat-Jehuda,

Israel [73] Assignee: Bayer Aktiengesellschaft,

Leverkusen, Germany [22] Filed: Apr. 5, 1973 [21] App]. No.: 348,419

[30] Foreign Application Priority Data Apr. 20, I972 Germany 2219397 [52] US. Cl 259/36, 259/4, 259/DIG. l7 [5]] Int. Cl BUM 13/02 [58] Field of Search 259/4, 18, 36, 95, DIG. 17

[56] References Cited FOREIGN PATENTS OR APPLICATIONS 1,937,374 2/1971 Germany 259/DIG. 17

Primary Examiner-Peter Feldman Assistant Examiner-Alan Cantor Attorney, Agent, or FirmBurgess, Dinklage & Sprung 57] ABSTRACT A vessel is used for pneumatically mixing powdered or granular material, containing an elevating tube consisting of two individual tubes beneath which a gas inlet is arranged, the lower individual tube forming an annular channel with the wall of the vessel and, in the event of a given drop in pressure in the elevating tube, the length of this annular channel is adapted to the pressure drop in the elevating tube in such a way that at least substantially the same pressure drop which prevails over the length of the elevating tube, prevails over the length of the annular channel.

5 Claims, 2 Drawing Figures PATENTEBHARWIENS 1 3,871,626

sume nrz VESSEL FOR PNEUMATICALLY MIXING POWDERED R GRANULAR MATERIAL This Patent application bases on Patent application Ser. No. 155,362, filed June 21, 1971 now U.S. Pat. No. 3756,5 69 which is a continuation-in-partapplication of Patent application Ser. No. 49,883, filed June 25, 1970, now abandoned.

The present invention relates to a vessel for pneumatically mixing powdered or granular material.

A known vessel of the above type comprises a conical base with a bottom outlet and a gas inlet situated therein and above which an elevating tube is arranged which terminates in the upper part of the vessel and which is divided into at least two separate tubes, the upper end of the lower tube being widened in the upward direction and surrounding-the lower end of the upper tube with an annular channel therebetween.

The advantages of such mixing vessels are that they are easy to clean, do not have any complicated fittings and provide for effective longitudinal and transverse mixing over a short mixing time.

It has been found, however, that such mixing vessels use a considerably quantity of air in operation.

Accordingly, it is the object of the present invention to improve the mixing vessel in such a way that the air consumption is considerably reduced.

According to the present invention, there is provided a vessel for pneumatically mixing powdered or granular material the vessel comprising a conical base with a bottom outlet and a gas inlet situated therein and above which an elevating tube is arranged which terminates in the upper part of the vessel and which is divided into at least two separate tubes, the upper end of the lower tube being widened in the upward direction and sur' rounding the lower end of the upper tube leaving an annular channel therebetween, the lower tube forming a second annular channel with the wall of the vessel the second annular channel being adapted so that in use the drop in pressure over the length of the elevating tube is at least substantiallythe same as the drop in pressure over the length of the annular channel.

This structural measure reduces the air requirement very considerably.

In one particular embodiment of the vessel according to the invention, the lower tube is in the form of a displacement body. By this type of design, the annular channel required between the wall of the vessel and the lower tube can be adjusted to meet particular requirements.

Alternatively, the wall of the vessel in the vicinity of the lower individual tube approimates the contour of the lower individual tube. In both cases, the effective length of the annular channel, the so-called braking zone," determines the required pressure drop.

The inlet of the upper tube which is arranged above the lower tube preferably extends down to a point near the inlet of the lower tube. Compared with the original embodiment according to the U.S. Pat. No. 3,756,569, where the upper tube does not extend so far into the lower tube, the present embodiment has the advantage that only a small plug which can be broken up with relatively little energy is formed when the mixer is started. It is sufficient for this purpose to use a fan whose output is adapted to the mixing operation. In the previous embodiment, the fan had to be designed to provide a relatively high pressure because more energy was required for the starting of the mixer than in its normal operation.

In another embodiment of the mixing vessel according to the invention, the cross-section of the second annular channel is selected so that a given proportion of the total quantity of air is passed therethrough in such a way that the loosening speed is not exceeded. The loosening speed is the rate of air flow which is required to fluidise the material to be mixed. The quantity of air passed through the second annular channel is referred to as the so-called false-air quantity. This quantity is normally so large as to be disadvantageous because it causes an excessive air requirement. However it is often desirable in the mixing of different materials for some of the air not to flow through the elevating tube but to rise upwards through the material in the container. outside the elevating tube. The material is readily loosened in this way. However, the loosening rate should not be exceeded because otherwise the material flows too quickly towards the bottom outlet.

Two embodiments of mixing vessels according to the invention are described by way of example in the following with reference to the accompanying drawings, wherein FIG. 1 is a section through a mixing vessel with a lower tube in the form of a displacement body.

FIG. 2 is a section through a mixing vessel with a wall adapted to the contour of the lower tube.

The mixer shown in FIG. 1 consists of a cylindrical vessel 1 with a conical base 2 and a removable cover 3. An elevating tube which consists of a conical lower tube 4, in the form ofa displacement body, and a cylindrical upper tube 5, is fixed in the vessel 1, by means of stays 7a and 7b. The two separate tubes 4 and 5 of the elevating tube are fitted into one another with an annular channel 6 therebetween. The tube 5 is provided with radially arranged spacer ribs 9 for centring it in the conically widened lower tube 4. Together with the wall of the vessel 1, the lower tube 4 forms a second annular channel 8 in the vicinity of the conical base 2. The length of this annular channel 8 which is effective as the braking zone is denoted by the reference A. The pressure drop in the braking zone A corresponds to the pressure drop from the inlet of the: elevating tube to its outlet. In other respects, this embodiment of the mixing vessel corresponds to that of the Parent Application.

The mixer illustrated in FIG. 2 consists of a cylindrical vessel 1 with a conical base 2 which is divided into differently tapering sections 2a, 2b and 2c. The vessel 1 has a removable cover 3'. An elevating tube which consists of a conical lower tube 4 and of a cylindrical upper tube 5' is fixed in the vessel 1 by means of stays 7a and 7b. The two separate tubes 4' and 5 of the elevating tube are fitted into one another with an annular channel 6 therebetween. The upper tube 5 is provided with spacer ribs 9' welded radially on to it for centring it in the conically widened tube 4. Over the length A which is effective as a braking zone the lower tube 4 forms an annular channel 8 with the conical base section 2b.

In both of the embodiments shown in FIGS. 1 and 2 the cross-section of the annular channel 8, 8 is constant over the effective braking zone A, A. By selecting the cross-section, it is possible to determine how much of the quantity of gas supplied is to pass through the annular channel 8, 8.

EXAMPLE 1 The mixer shown in FIG. 1 has a capacity of 50 The material to be mixed has a grain size of 3 X 3 X 3 mm, and a specific gravity of 1,100 kg/m. The elevating tube is metres tall. The total quantity of air supplied amounts to 7,800 m /hour, of which 800 m lhour pass through the annular channel 8 as so-called false air. The effective braking zone A is 1.7 metres long. The loosening rate of the air in the case of the aforementioned material to be mixed amounts to 2.25 m/second and should not be exceeded. Accordingly, a loosening rate of 0.8 m/second was selected. Under these conditions the annular channel has a cross-sectional area of 0.28 m

Without the braking zone A, the quantity of false air which would rise upwards in the vessel 1 alongside the elevating tube would be a few hundred persent greater. In order to be able to operate the vessel at all, it would thus be necessary to introduce a considerably greater overall quantity of air than in the above Example.

EXAMPLE 2 The mixer has the same parameters and is operated under the same conditions as in Example 1, but is in the form of the embodiment shown in FIG. 2. For a required quantity of false air of 800 m /hour, the freecross-section of the annular channel 8 also amounts to 0.28 m in this case.

Without the braking zone 8 the same disadvantages would arise as in operation of the mixer according to FIG. 1 and Example 1. If it is desired to operate the mixers of FIGS. 1 and 2 under the same conditions as in Examples 1 and 2 but with a required quantity of false air of 1,600 m /hour the free cross-section of the annular channel 8, 8 would have to amount to 0.56 m

What we claim is:

l. A vessel for pneumatically mixing powdered or granular material comprising a conical base with a bottom outlet and a gas inlet situated therein and within which an elevating tube is mounted, which terminates in the upper part of the vessel and which comprises an upper tube and a lower tube, an upper end portion of the lower tube being widened in the upward direction and surrounding the lower end of the upper tube leaving an annular channel therebetween, the lower tube forming a second annular channel with the wall of the vessel, the second annular channel having a cross sectional area such that in use the drop in pressure over the length of the elevating tube is at least substantially the same as the drop in pressure over the length of the second ann'ular channel.

2. A vessel according to claim 1, wherein the lower tube is in the form of a displacement body.

3. A vessel according to claim 1, wherein the wall of the vessel follows the contour of the lower tube in the vicinity thereof.

4. A vessel according to claim 1 wherein the inlet of the upper tube extends downwards to a point near the inlet of the lower tube.

5. A vessel according to claim 1 wherein for a required proportion of the total quantity of air to be passed through the second annular channel of the cross-section of this annular channel is selected in such a way that the loosening rate is not exceeded. 

1. A vessel for pneumatically mixing powdered or granular material comprising a conical base with a bottom outlet and a gas inlet situated therein and within which an elevating tube is mounted, which terminates in the upper part of the vessel and which comprises an upper tube and a lower tube, an upper end portion of the lower tube being widened in the upward direction and surrounding the lower end of the upper tube leaving an annular channel therebetween, the lower tube forming a second annular channel with the wall of the vessel, the second annular channel having a cross sectional area such that in use the drop in pressure over the length of the elevating tube is at least substantially the same as the drop in pressure over the length of the second annular channel.
 2. A vessel according to claim 1, wherein the lower tube is in the form of a displacement body.
 3. A vessel according to claim 1, wherein the wall of the vessel follows the contour of the lower tube in the vicinity thereof.
 4. A vessel according to claim 1 wherein the inlet of the upper tube extends downwards to a point near the inlet of the lower tube.
 5. A vessel according to claim 1 wherein for a required proportion of the total quantity of air to be passed through the second annular channel of the cross-section of this annular channel is selected in such a way that the loosening rate is not exceeded. 